In movies or the like, a progressive-form image signal made of successive images of 24 frames per one second is used. On the other hand, in television image signals, an image signal made of successive images of 30 frames/second format is often used. In television image signals, both a progressive form and an interlace form are used.
The 2-3 pulldown conversion method is known in the art as a technique for converting a progressive image signal of 24 frames/second format (hereinafter referred to as 24 progressive signal) into an image signal of 30 frames/second format.
Hereinafter, a conversion process using the 2-3 pulldown conversion method will be described with reference to FIG. 14. Here, as one example thereof, a process of converting a 24 progressive signal into an interlace-form image signal of 30 frames/second format (hereinafter referred to as 30 interlace signal) will be described.
First, referring to FIG. 14(a), frame images of a 24 progressive signal located at the first image position (frame A) are subjected to a conversion process by being allotted to two field images of a 30 interlace signal at the first image position (the first field images F1, F2), as shown in FIG. 14(b). Further, frame images of the 24 progressive signal located at the next image position (as viewed from the first image position) (frame B) are subjected to a conversion process by being allotted to three field images located at the next position of the 30 interlace signal (the next field images F1, F2, F1).
Such a conversion process is repeated every 1/12 second, thereby two frames of the 24 progressive signal (images for 2/24 seconds) are arranged to correspond to five fields of the 30 interlace signal (images for 5/60 seconds). Then, a conversion process including this corresponding process as one sequence is repeatedly executed. Hereinafter, an image signal obtained by such a conversion process will be referred to as a 2-3 pulldown interlace signal.
A general signal form used for editing work or the like is a 30 interlace signal. However, the time code used in reproducing and outputting from a recording reproducing medium having a 24 progressive signal recorded thereon (hereinafter referred to as 24-time code) cannot be used in an image process of a system that uses a 30 interlace signal. For this reason, in carrying out the 2-3 pulldown conversion process, the following process becomes essential. Namely, a 24-time code is extracted from a recording reproducing medium having a 24 progressive signal recorded thereon. The extracted 24-time code is then converted into a time code used in reproducing and outputting from a recording medium having a 30 interlace signal recorded thereon (hereinafter referred to as 30-time code).
In the meantime, a technique of generating and outputting a 30-time code in ordinary reproduction of a 2-3 pulldown interlace signal is known in the art. However, in a system that involves variable-speed reproduction, one cannot output a 30-time code ceaselessly and accurately in correspondence with a 24-time code that is output by variable-speed reproduction from a recording reproducing medium having a 24 progressive signal recorded thereon. For this reason, the system construction will be difficult.